Chronic dialysis has been performed on patients with kidney failure since the early 1960's. The dialyzers or “artificial kidneys” that made this possible were a result of a technical evolution that began in the 1930's and 1940's. A dialyzer is a device for cleansing blood through hemodialysis by a process of diffusion and convection of waste products, dissolved solutes and fluid from the blood across a semi-permeable membrane into a dialysis solution known as dialysate. A dialyzer system is an assembly comprising the dialyzer and associated equipment to support the dialyzer, such as plumbing and pumps.
The first dialyzer systems used were made of a large rotating drum that used sausage casing as a semi-permeable membrane wrapped over a large round, wooden frame. Blood was routed through the casing and the casing was bathed in dialysate solution. By the 1970's the industry had developed the hollow fiber dialyzer. This device is made of 10,000-14,000 hollow semi-permeable membrane fibers housed in a tube 30 cm long and 6 cm in diameter, yet providing up to two square meters of surface area for blood flowing within the fibers to interface with dialysate flowing around the outside of the fibers. Though the hollow fiber dialyzers of today are a bit more efficient, the technology has not changed significantly since this time.
The hollow fiber dialyzer has a mal-distribution of dialysate flow due to uneven and inconsistent spacing between individual fibers. Areas with stagnant flow as well as areas with developed shunt flow dramatically reduce the efficiency of the mass transfer on the dialysate side. The spacing between individual fibers is generally small, thus diffusion is an important mechanism of mass transfer in the inter-fiber space. Improvement of diffusion, and hence improved dialysate usage efficiency is limited due to the inherent physical character of the hollow-fiber dialyzers.
Currently, hollow fiber dialyzers use 120-200 liters of dialysate solution, comprising predominantly water, to perform a dialysis treatment. A relatively large quantity of dialysate solution is used because the flow of dialysate is haphazard around the fibers. The need for this quantity of dialysate solution requires that dialysis machine be quite large. The water used for dialysis must also be purified of chemical and microbiological contamination which adds to the amount of equipment and the technical expertise needed to perform dialysis treatments.
As a result of the reliance on this complicated equipment, most dialysis treatments are performed at dialysis centers staffed by a team of professionals. Less than one percent of hemodialysis patients perform their own treatments at home. In a center, dialysis treatments are performed in a very rapid manner over a short period of time. Each patient receives three treatments per week. Studies have shown that there is a great improvement when patients are dialyzed slower, longer, and more often. Not only are the patient outcomes much better, the overall cost of their care is less due to reductions in medication and hospitalization costs.
The only economically viable way for patients to receive more frequent dialysis treatments is for them to perform their own dialysis treatments at home. To make this technically feasible it is necessary to improve the technology such that dialysis machines are smaller, more portable, consume less water, and be simpler for the lay person to operate.
What is needed in the art is a dialyzer with improved efficiency of mass transfer across the dialysis membrane that separates the blood from the dialysate solution.